Means for securing planar member to cathode ray tube faceplate

ABSTRACT

A planar member such as a phosphor coated fiber optic plate, having a thermal coefficient of expansion that is incompatible with that of a cathode ray tube envelope and faceplate, is accurately supported a precise distance from the inner surface of the faceplate by a plurality of step-shaped supports having a spacer portion disposed between the planar member and faceplate and a shoulder portion adjacent to the periphery of the planar member. A conductive disc having an opening therein is situated adjacent to the planar member so that a plurality of fingers which project inwardly from the opening contact the peripheral portion of the planar member. Means are provided for securing the disc to the supports in such a manner that the fingers apply a retaining force to the planar member and make electrical contact thereto.

- United States v Netti Steinberg'et al.

75 Inventors: David R. Steinberg; William T. sm- 11 ton, both of Raleigh, NC.

[73 Assignee: Corning Glass Worlts, Corning,

[22] Filed: Nov. 116, 1970 [21] Appl. No.: 89,715

[52] U.S. Cl. ..3l3/91, 313/92, 313/286 [51] lint. C1. ..H0lj 29/112,1'1011' 29/02, H0lj 19/50 [58] Field of Search ..3 13/92 LP, 65 LF,

I 3.1 3/92 PD, 85 S, 92 R [56] I References Cited UNITED STATES PATENTS 2,172,775 9/1939 'Schmidt-Ott et al. ..313/92 X 2,781,469 2/1957, Van Bree et al ..3l3/92 R 2,856,552 10/1958 Evans ..3l3/92 PD 3,404,303 10/1968 Levin ..3l3/85 S 3,519,742 7/1970 Bjellandur... ..350/l60PX 3,038,096 6/1962 Knochel et a1. ..3l3/85 S 3,502,942 3/1970 'Khan et al.- ..3l3/85 S X 3,507,551 4/1970 1 Stetten ..3!3/92 LF 1451 Apr. 111, 1975 3,564,195 2/1971 Ploog ..3l3/85 S FOREIGN PATENTS OR APPLICATIONS 108,845 10/1943 Sweden ..313/92 R Primary Examiner-Robert Segal AttorneyClarence R. Patty, Jr., Walter S. Zebrow$1 i and William J. Simmons, Jr.

[5 7] ABSTRACT A planar member such as a phosphor coated fiber optic plate, having a thermal coefficient of expansion that is incompatible with that of a cathode ray tube envelope and faceplate, is accurately supported a precise distance from the inner surface of the faceplate by a plurality of step-shaped supports having a spacer portion disposed between the planar member and faceplate and a shoulder portion adjacent to the periphery of the planar member. A conductive disc having an opening therein is situated adjacent to the planar member so that a plurality of fingers which project inwardly from the opening contact the peripheral portion of the planar member. Means are provided for securing the disc to the supports in such a manner that the fingers apply a retaining force to the planar member and make electrical contact thereto.

7 8Claims, 3 Drawing Figures MEANS FOR SECURING PLANAR MEMBER To. CATHODE RAY TUBE FACEPLATE BACKGROUND OF THE INVENTION This invention relates to means for mounting a planar member in the path of an electron beam within a tube screens, masks, targets or like members, the thermal expansion coefficients of which are not compatible with that of the envelope glass. In some instances it is not advisable to directly seal the member to the envelope or to the faceplate.

One such member, the thermal coefficient of expansion of which is not compatible with that of the tube envelope, is a fiber optic plate. U.S. Pat. No. 3,335,310 issued Aug. 8, I967 to RJ. Ney discloses a typical example of the manner in which a fiber optic faceplate is sealed to a tube envelope. A thin metal annulus or cylinder is sealed to one end of the tube envelope and a thin metal flange or frame member having a concentric opening therein for receiving the fiber optic faceplate is welded to the metal cylinder. In addition to requiring a plurality of glass to metal seals, the following disadvantages arise from utilizing a fiber optic plate as'the SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide means for supporting a member such as a phosphor coated target, mask or the like a precise distance from the inner surface of a cathode ray tube faceplate.

Another object of the present invention is to provide improved means for making electrical contact to a 0 member supported within a cathode ray tube.

faceplate. Fiber optic plates generally exhibit structural weakness, poor heat resistance and poor hermeticity. Moreover, the size and shape of a fiber optic plate may be such as to render itunsuitable for use as a faceplate. For example, some fiber optic plates must be relatively thin in order to provide optimum optical properties and therefore lack sufficient strength to be used as ,a faceplate.

Supporting means of the type used to support a shadow mask adjacent to a mosaicscreen of phosphor dots in a cathode-ray color tube have been considered as a means for supporting a phosphor coated fiber optic plate adjacent to the cathode ray tube faceplate; however, this type of supporting means, which supports themask from the sidewalls of the tube envelope. near the faceplate cannot support the; fiber optic plate the required distance from the faceplate with a high degree of accuracy. H

- In our co-pending application .Ser. No. 89,769 entitled Means for Securing Planar Member to Cathode Ray Tube Faceplate and'filed on even date herewith, now U.S. Pat. No. 3,660,706 there is disclosed apparatus for accurately mounting a planar member adjacent to the inner surface of a cathode ray tube faceplate. That apparatus consists of slotted glass posts which are used for supporting a planar member a precise distance from the faceplate. Spring contact means affixed to at least one of the glass posts applies a retaining force to the planar member and makes electrical contact thereto. The present invention is an improvement overthe invention disclosed in the aforementioned application for the following reasons. It is more rugged, easier to assemble, and provides more accurate target'to-faceplate spacing, especially for small separations. The present invention also provides better electrical contact to the planar member. Moreover, the support means of the present invention is easier to as semble and disassemble so that the planar member is more easily reclaimed in the event of a tube failure.

A further object of the present invention is to pro- "vide an easily assembled apparatus for supporting a planar member within a cathode ray tube.

A more specific object of the present invention is to provide an apparatus for accurately positioning a photochromic fiber optic plate with respect to a lensshapedcathode ray tube faceplate.

Briefly, the cathode ray tube in accordance with the present invention includes an evacuated envelope having means therein for producing an electron beam and a faceplate for viewing an optical image produced by the beamQA planar member is disposed a predetermined distance from the inner surface of the faceplate by support means. A thin conductive member having an opening therein approximating the size and shape of the planar member is disposed adjacent to the planar member. Contact means on the thin conductive member applies a retaining force to the planar member and makes electrical contact therewith. Means are provided for attaching the thin conductive member to the support means, and means are provided for applying an electrical potential to the thin conductive member.

- I BRIEF DESCRIPTION OF THE DRAWINGS 5 1 FIG. 1 is a view in partial cross-section of a cathode '2 ofFIG. 1.

FIG. 3 is an enlarged, cross-sectional view taken along lines 3-3 of FIG. 2.

DETAILED DESCRIPTION FIGS. 1 and 2 show a conventional cathode ray tube bulb or envelope comprising the usual constricted neck portion 2, flared portion 4 and end portion 6 against which a lens-shaped faceplate 8 is sealed. An electron source 10, positioned in the constricted portion 2, may comprise conventional means for providing at least one electron beam represented by the dashed line 12. A contact terminal or anode button 18 provides an electrical connection to an internal conductive wall coating 20.

A planar member such as a phosphor coated target 22 is accurately spaced a predetermined distance from faceplate 8 by a plurality of step-shaped supports 24 having aspacer portion 26 disposed between member 22 and faceplate 8 and a shoulder portion 28 adjacent the periphery of target 22, as shown in FIG. 3. At least two supports are required, and in the disclosed embodiment six supports are used. If the supports are too long, a stress may be induced in the faceplate. Therefore, two supports are used along the longer sides of the target 22 rather than one long support. Supports 24 may be made from glass or glass ceramic or from a metal such as a nickel-copper-chrome alloy which has a thermal coefficient of expansion similar to that of the faceplate. In a preferred embodiment, a nickel-copperchrome alloy support was used to space the target 0.5 mm from the faceplate.

Since the distance between target 22 and faceplate 8 must be accurately controlled, no bonding material should be located between the supports and the faceplate. The supports are therefore thoroughly cleaned and positioned directly onto the faceplate by a dummy substrate of correct dimensions and expansion coefficient or by some other holding device. Glass solder 30 is then placed around the base of the sup ports, and this assembly is placed in a furnace and baked at 440C. for 1 hour. The temperature should be increased to 440C. at a rate of lC./min. After the one-hour bake at 440C., the temperature is decreased to 350C. at a rate of about 1 /&"C/min. and thereafter reduced to room temperature at a rate of about 6C./mi n. A solder glass is selected which has a thermal coefficient of expansion that is compatible with that of the faceplate glass. A lead-zinc-borate glass of the type described in US. Pat. No. 2,889,952 issued-to S.A..

Claypoole may be used.

An enlarged cross-sectional view of a portion of the target 22 is shown in FIG. 3. In this embodiment, the target 22 consists of a photochromic fiber optic plate 35 on which there is deposited a dichroic layer 38, a phosphor layer 40 and an aluminum layer 42. The phosphor layer 40 does not extend to the periphery of the target and a peripheral portion 44 of the aluminum layer is deposited directly on dichroic layer 38. It is not intended that this invention be limited to the target illustrated in FIG. 3. Other targets such as phosphor coated plates of conventional glass, homogeneous photochromic glass or conventional fiber optic plates, or other planar members such as screens, masks or the like could be supported in accordance with the present invention.

The dummy substrate is replaced by the target 22, and a thin conductive member such as disc 48 having slots 56 therein is lowered to target 22, guided by passing through each of the slots 56 a tab 50, which is welded or otherwise affixed to each of the supports 24. A slight pressure is applied to the disc and the tabs are bent over to hold the disc firmly to the supports. Electrical contact is made between the peripheral portion 44 of target 22 and disc 48 by a plurality of fingers 52 which extend inwardly from an opening 54 which is approximately the size of target 22. Disc 48 may be fabricated from stainless steel or some other type of vacuum quality metal. The contact fingers 52 may be coated with a thin layer of graphite, gold or the like to insure good contact to the target.

After completing the faceplate assembly, the envelope is lowered onto the faceplate, and spring contacts 58, which are attached to disc 48, are biased against conductive coating 20, thereby completing the electrical connection from the coating to target 22. The envelope end portion 6 is then glass-soldered to faceplate 8 in a conventional manner.

After the faceplate is sealed to the envelope end portion 6, the entire cathode ray tube is placed in a vacuum system and a coating of conductive material such as aluminum is evaporated onto flared portion 4, end portion 6, target 22 and that part of faceplate 8 that is not in the shadow of the target. This can be accomplished by inserting the evaporating source into the neck portion 2. For the sake of clarity the only conductive coating illustrated as resulting from this process is coating 62 on the faceplate, since the envelope walls and the target were previously coated with conductive material. Aluminum coating 62 provides a reflecting surface on that part of the faceplate not occupied by target 22. This reflecting surface aids in bleaching photochromic glass in the target 22. The aluminum coating deposited on flared portion 4 also insures good electrical contact between the anode button 18 and the conductive coating 20.

The fiber optic plate 35 of FIG. 3 is made up of many very fine individual fibers 36 which are joined by fusion in side-by-side relation with each other, the ends of these fibers forming two planar surfaces of the plate 35. Each of the fibers 36 consists of a core of a light transmitting medium having a relatively high index of refraction surrounded by a relatively thin cladding of glass having a relatively low index of refraction. The cores of the fibers are made from photochromic glass, which has the property of becoming less transparent when irradiated with blue or ultraviolet light, remaining unaffected by green light and becoming more transparent when irradiated by infrared, red or orange light. The characteristics and production of such glass are described in US. Pat. No. 3,208,860 granted to W.H. Armistead and SD. Stookey on Sept. 28, 1965. The cladding glass may consist of that which is taught in US. Pat. No. 2,382,056 granted to HP. Hood on Aug. 14, 1945.

The dichroic layer 38 transmits ultraviolet light having a wavelength around 350 nm and reflects light having a wavelength above 450 nm. The layer 38 is typically multilayered and may be formed by well known evaporating techniques. Phosphor layer 40 is selected for the wavelength of light which it radiates when excited by the electron beam. The light radiated by the phosphor is preferably ultraviolet light which passes through dichroic layer 38 and darkens photochromic fibers 36 on which it impinges. Selected portions of the photochromic fiber optic plate 35 may be darkened by controlling the position and intensity of the electron beam to write and store information therein.

Referring to FIGS. 1 and 3, information stored in the target 22 is read therefrom by directing onto faceplate 8 a beam of green light represented by the arrows 76. This probing light is focused by the lens-shaped faceplate onto fibers 36, passes therethrough, reflects from dichroic layer 38 and again passes through fibers 36. The resultant image may be projected by a lens system which includes faceplate l6. Mounting the target 22 to the faceplate 16 in the manner disclosed herein provides the accurate positioning that is necessary to insure that the target is properly centered with respect to the faceplate and properly spaced therefrom thus permitting the accurate positioning of the target in the optical system.

We claim:

1. A cathode ray tube comprising an evacuated envelope,

means in said envelope for producing an electron beam,

a faceplate forming part of said envelope,

those a glass plate disposed adjacent the inner surface of said faceplate,

a layer of phosphor disposed on that surface of said glass plate which is .remote from said faceplate, said phosphor layer being so disposed in said envelope that it is adapted to receive electrons from said electron beam producing means,

i a conductive layer disposed upon the surface of said phosphor layer,

a plurality of support means affixed to said faceplate and spaced around the periphery of said glass plate for disposing said glass plate a distance from said faceplate, a portion of each of said support means extending between said glass plate and said faceplate, I

a thin conductive member having an opening therein approximating the size and shape of said glass plate,

a plurality of conductive fingers projecting inwardly from the periphery of the opening defining portion of said thin conductive member, said fingers mak-' ing electrical contact with a peripheral portion of said conductive layer and applying a retaining force to said glass plate, said conductive member having a plurality of slots, Y means for attaching said conductive member to said support means including a plurality of tabs attached to said support means and extending through said slots and bent over to apply a retaining force to said conductive member, and means to apply an electrical potential to saidconductive member. 2. A cathode ray tube in accordance with claim 10 wherein said. support means comprises a plurality of step-shaped supports having a spacer portion disposed between said glass plate and said faceplate anda Y shoulder portion disposed adjacent the peripheral portion of said glass plate.

3. A cathode ray tube in accordance with claim which further comprises a conductive coating disposed on a portion of the inner surface of said envelope, said means to apply an electrical potential comprising at least one conductive spring contact extending between said conductive member and said conductive coating.

wherein said glass plate is a fiber optic plate.

7. A cathode ray tube in accordance with claim 6 wherein said fiber optic plate comprises a plurality of fibers in side-by-side relation with each other, the ends of said fibers forming two planar surfaces, each fiber consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core.

8. A cathode ray tube comprising an evacuated envelope,

a faceplate forming part of said envelope,

a fiber optic plate disposed adjacent the inner surface of said faceplate said fiber 0 tic plate comprising a plurality of fibers m sldey-slde relation with each other, the ends of said fibers forming first and second opposed planar surfaces, said first surface being disposed adjacent to said faceplate, each of said fibers consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core, a plurality of step-shaped supports for disposing said fiber optic plate a distance from said faceplate, each of said supports having a spacer portion disposed between said fiber optic plate and said faceplate and a shoulder portion disposed adjacent the peripheral portion of said fiber optic plate, a connecting tab affixed to at least two of said supports, a thin conductive member having an opening therein approximating the size and shape of said fiber optic plate,

a plurality of conductive fingers projecting inwardly from the periphery of the opening defining portion of said thin conductive member, said fingers making electrical contact with a peripheral portion of said conductive layer,

a layer ofphosphor disposed on said second surface of said fiber optic plate,

a conductive layer disposed upon the surface of said phosphor layer,-

a plurality of slots in said conductive member, each of said slots being aligned with a corresponding one of said tabs, each of said tabs extending through a corresponding one of said slots and being bent to secure said conductive member in such a manner that said fingers exert a retaining force against said fiber optic plate, and

means to apply an electrical potential to said conductive member.

l lk 

1. A cathode ray tube comprising an evacuated envelope, means in said envelope for producing an electron beam, a faceplate forming part of said envelope, a glass plate disposed adjacent the inner surface of said faceplate, a layer of phosphor disposed on that surface of said glass plate which is remote from said faceplate, said phosphor layer being so disposed in said envelope that it is adapted to receive electrons from said electron beam producing means, a conductive layer disposed upon the surface of said phosphor layer, a plurality of support means affixed to said faceplate and spaced around the periphery of said glass plate for disposing said glass plate a distance from said faceplate, a portion of each of said support means extending between said glass plate and said faceplate, a thin conductive member having an opening therein approximating the size and shape of said glass plate, a plurality of conductive fingers projecting inwardly from the periphery of the opening defining portion of said thin conductive member, said fingers making electrical contact with a peripheral portion of said conductive layer and applying a retaining force to said glass plate, said conductive member having a plurality of slots, means for attaching said conductive member to said support means including a plurality of tabs attached to said support means and extending through said slots and bent over to apply a retaining force to said conductive member, and means to apply an electrical potential to said conductive member.
 2. A cathode ray tube in accordance with claim 10 wherein said support means comprises a plurality of step-shaped supports having a spacer portion disposed between said glass plate and said faceplate and a shoulder portion disposed adjacent the peripheral portion of said glass plate.
 3. A cathode ray tube in accordance with claim 2 which further comprises a conductive coating disposed on a portion of the inner surface of said envelope, said means to apply an electrical potential comprising at least one conductive spring contact extending between said conductive member and said conductive coating.
 4. A cathode ray tube in accordance with claim 3 wherein said evacuated envelope is circular in cross-section and said conductive member comprises a disc, the circumference of which contacts said conductive coating.
 5. A cathode ray tube in accordance with claim 3 wherein said faceplate is lens-shaped.
 6. A cathode ray tube in accordance with claim 5 wherein said glass plate is a fiber optic plate.
 7. A cathode ray tube in accordance with claim 6 wherein said fiber optic plate comprises a plurality of fibers in side-by-side relation with each other, the ends of said fibers forming two planar surfaces, each fiber consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core.
 8. A cathode ray tube comprising an evacuated envelope, a faceplate forming part of said envelope, a fiber optic plate disposed adjacent the inner surface of said faceplate, said fiber optic plate comprising a plurality of fibers in side-by-side relation with each other, the ends of said fibers forming first and second opposed planar surfaces, said first surface being disposed adjacent to said faceplate, each of said fibers consisting of a core of photochromic glass having a given index of refraction surrounded by a cladding of glass having an index of refraction lower than that of said core, a plurality of step-shaped supports for disposing said fiber optic plate a distance from said faceplate, each of said supports having a spacer portion disposed between said fiber optic plate and said faceplate and a shoulder portion disposed adjacent the peripheral portion of said fiber optic plate, a connecting tab affixed to at least two of said supports, a thin conductive member having an opening therein approximating the size and shape of said fiber optic plate, a plurality of conductive fingers projecting inwardly from the periphery of the opening defining portion of said thin conductive member, said fingers making electrical contact with a peripheral portion of said conductive layer, a layer of phosphor disposed on said second surface of said fiber optic plate, a conductive layer disposed upon the surface of said phosphor layer, a plurality of slots in said conductive member, each of said slots being aligned with a corresponding one of said tabs, each of said tabs extending through a corresponding one of said slots and being bent to secure said conductive member in such a manner that said fingers exert a retaining force against said fiber optic plate, and means to apply an electrical potential to said conductive member. 